People pay more attention on housing security with social progress and technical development. A door closer, usually mounted between the door and the door frame, will close the door automatically under the resilient restoring force of the door closer, ensuring that the door is returned to the original position accurately and timely after the door is open, which provides convenience in daily life.
However, the door closer in the prior art usually generates a large impact force when closing the door, whereby people are easily bumped by the door because they cannot timely dodge, or escape the closing door. Also, sometimes a big impact noise will occur when the door is closed.
In order to solve these problems, a hydraulic door closer has been used to control the door opening/closing by regulating the flow rate of hydraulic oil, whereby the process of opening/closing the door could be adjusted to adapt the requirements of users, while protecting the door and the door frame from damage.
A key factor to guarantee the normal operation of the hydraulic door closer is sealing of the door closer. When the hydraulic oil expands due to increased temperature, the sealing element inside the door closer will be squeezed, whereby the hydraulic oil may leak and the door closer may be destroyed, or some unwanted situation will occur, e.g., a gap will appear during opening/closing door, people will be bumped while closing the door, etc.
Therefore, a primary objective of the present invention is the provision of an improved hydraulic door closer which overcomes the problems of the prior art.
Another objective of the present invention is the provision of a hydraulic door closer having a hydraulic fluid compartment with a variable volume.
A further objective of the present invention is the provision of a method for controlling internal pressure of a hydraulic door closer.
These and other objectives will become apparent from the following description of the invention.